PL163591B1 - Method of obtaining novel derivatives of 4-phenyl-4-piperidinecarboxyamide - Google Patents

Abstract

Compounds of the formula IV for use as local anaesthetica and analgetica, as well as a method for their preparation, their pharmaceutical preparations and their use. <IMAGE> IV

Description

The subject of the invention is a process for the preparation of new 4-phenyl-4-piperidinecarboxamide derivatives showing local anesthetic and analgesic effects. They can find use in the production of pharmaceutical preparations.

Pethidine is a commonly used pain reliever. It also has a weak local anesthetic effect. Both the anesthetic and analgesic effects of pethidine after spinal administration are generally insufficient. Instead, combinations of bupivacaine with fentanyl or morphine are used. Opium-containing painkillers have several serious drawbacks, such as the development of tolerance and addiction, and the risk of respiratory depression. Thus, there is a need for agents that induce local anesthesia with the remaining analgesic effect. Such agents should be used intraoperatively as local anesthetics after spinal or epidural injections. The compounds below provide good post-operative pain relief.

D. J. Hardy et al. described in J. Med. Chem. 8, pp. 847-851 (1965), the structure-activity relationship of certain pethidine analogues with analgesic effects. Swedish Patent No. 96,980 describes 1-methyl-1-phenylpiperidine-4-carboxylic acid and its two amides. This document only mentions that the compounds can be used in the manufacture of new drugs, without mentioning any particular pharmacological activity. French Patent No. 2,156,470 discloses 1- (3,3-difer-ylpropyl) piperidine derivatives which, due to their high lipid solubility, can only be active as analgesics, and as local anesthetics. Some 1-butyl-4-phenyl-4-piperidinecarboxylic acid amides are described in Acta Pol. Pharm. 1979.36 (4), pp. 439-4, (Chemical Abstracts 93/1980

163 591 3 (7970v). These amides have an analgesic effect but have no local anesthetic effect.

It has been found that the compounds of the formula IV and their pharmacologically acceptable salts not only show surprisingly good activity as spinal and epidural anesthetics, but also have an additional analgesic effect that lasts a long time after the anesthetic effect has worn off. Thus, there is no need to administer a combination of active agents, thus avoiding the risks mentioned above. The present invention relates to a process for the preparation of compounds of general formula 4 in which R 1 is an alkyl group of 2 - 6 carbon atoms or an alkoxyalkyl group of the formula R4O- (CH2) ™ - in which R4 is an alkyl group of 1 to 4 carbon atoms, and equals 2, 3 or 4, R2 and R3 are independently of each other an alkyl group of up to 6 carbon atoms, or R2 and R3 form a chain of formula (CH2) _n , where n is 4.5 or 6, or one of R2 and R3 is hydrogen and the other is a straight or branched alkyl group of 1-6 carbon atoms, as well as their pharmacologically acceptable salts.

Preferred compounds according to the invention are those in which R1, R2 and R3 are alkyl groups.

Especially preferred are compounds in which R1 is hexyl, R2 is methyl or ethyl and R3 is an ethyl group.

Preferred salts according to the invention are pharmacologically acceptable salts. The hydrochloride is especially preferred.

According to the invention, the compounds of formula IV are prepared according to the reaction scheme shown in the figure in which A, Ri, R2 and R3 are as defined above.

Compounds of formula I, where A is CN or -CO2C2H5 and Ri is as defined above, are prepared from the corresponding secondary amine (Ri = H), except in which Ri is CH3 and A is CO2C2H5 and which is a commercially available compound called pethidine. Compounds of formula 2 are obtained directly from compounds of formula 1 wherein A is -CO2C2H5 (see example I) by reaction with an alkylamine, or are prepared as compounds of formula 4. Compounds of formula 4 are prepared by this method. that compounds of formula 1 are hydrolyzed to carboxylic acids of formula 3 and then the carboxylic acids of formula 3 are reacted with oxalyl chloride and the appropriate amine.

The invention is illustrated below by Examples 1-11, of which Examples 1-6 relate to the preparation of intermediates for the preparation of the compounds of formula 4, Examples VII-VIII relate to the preparation of compounds of formula 2, Example IX relates to the general process for the preparation of compounds of formula 4, Example X of pharmaceutical preparations, and Example XI of biological tests of new compounds. The abbreviation t.t. used in the examples. denotes the melting point, while t.c. boiling point.

EXAMPLE 1 Ethyl 1-hexyl-4-the; iyl- ^: 4-piperidine carboxylate hydrochloride.

Norpethidine (23.5 g, 0.10 mol), hexyl iodide (23.5 g, 0.11 mol) anhydrous Na 2 CO 3 (11.7 g, 0.11 mol) and acetonitrile (250 ml) were heated to reflux and stirred for 1.5 h. The mixture was filtered and the solvent was removed. The residue was dissolved in CH 2 G 2, the solution was washed with 100 ml of 1N NaOH and then with water and finally dried (K 2 CO 3). A solution of HCl gas in diethyl ether was then added, the solvents were removed and the residue was recrystallized from ethyl acetate. Yield 22.5 g of the hydrochloride with m.p. 156-158 ° C. M.p. according to J. Med. Chem. 8 pp. 847-851 (1965), 158 ° C.

Example II. Hydrochloride 1- [4 - ^^ oxybutyl] - '4 ^ f ^ ¢ ^ I ^ 2 ^ l <^^ - ^^ {^ iJ ^^ I ^ r ^ ^< d ^ l ^ ^< ^^^ Ethyl rbosylate ( compound of formula 1).

Norpethidine (15.63 g, 67 mmol), 4-ethoxybutyl chloride (10.67 g, 70 mmol), Na 2CO3 (7.77 g, 73 mmol), KI (0.6 g) and acetonitrile (150 ml) heated to reflux and stirred for 72 h. The mixture was filtered and the solvent was removed. The residue was dissolved in diethyl ether and the solution was washed with water and dried (MgSO4). Distillation gave 17.9 g of base, boiling at 160-163 ° C / 0.05 mm Hg. T.w. according to J. Chem. Soc. 3062 (1958) 180 ° C / 1 mm Hg. M.p. hydrochloride 143-145 ° C.

Example III. 1- (2-Ethoxyethyl) -4-cyano-4-phenylpiperidine (compound of formula 1).

The title compound was prepared as described in Example 2 from 4-cyano-4-phenylpiperidine and 2-bromoethyl ethyl ether without KI. Reaction time at reflux 6 hours. The compound boiled at 130-135 ° C / 0.005 mm Hg.

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Example IV. 1-Hexyl-4-phenyl-4-piperidinecarboxylic acid hydrochloride (compound of formula 3).

A mixture of the ethyl ester (22.5 g, 64 mmol), 20% hydrochloric acid (225 ml) and acetic acid (70 ml) was heated to reflux for 30 h. After cooling, the mixture was poured into 200 ml of ice-water, the acid was filtered and dried overnight. the air. Yield 12.9g. The filtrate was evaporated and the residue was treated with acetonitrile to give a further 4 g of acid. After recrystallization from acetonitrile, 16.9 g were obtained, m.p. 193-195 ° C. The acid contains the solvent from the crystallization.

ExampleV. 1- [4-Ethoxybutyl] -4-phenyl-4-piperidinecarboxylic acid hydrochloride (compound of formula 3).

A mixture of ethyl ester (17.9 g, 53.7 mmol), 2N NaOH (55 ml) and ethanol (6 ml) was heated to reflux with stirring for 24 h. The solution was extracted with diethyl ether and then acidified with dilute hydrochloric acid. The solvent was evaporated and the residue was extracted with acetone. The acetone solution was filtered and the solvent was evaporated. The crystalline residue was dried over CaCl2 in a vacuum desiccator and recrystallized from a THF-ethyl acetate mixture. Yield 11.7 g, mp. 131-133 ° C.

Example VI. 1- (2-ethoxyethyl) -4-phenyl-4-piperidinecarboxylic acid hydrochloride (compound of formula 3).

The cyanide mixture of Example 3 (5.5 g), KOH (5.5 g), ethanol (39 ml) and water (17 ml) was heated in an autoclave at 140 ° C for 6 hours. The reaction mixture was acidified with concentrated hydrochloric acid, the precipitated salt was filtered off, and the filtrate was evaporated. The residue was leached with hot acetone. 4.2 g of the title compound was obtained from the acetone extracts, mp. 150-155 ° C.

Example VII. N-Butyl-1-methyl-4-phenyl-4-piperidinecarboxamide (compound of formula 2).

Pethidine hydrochloride (2.56 g, 9 mmol) and butylamine (5 ml) were heated in an autoclave at 180 ° C for 3 days. The reaction mixture was shaken with 10 ml of 1N NaOH and diethyl ether and the ether extracts were dried (MgSO ₄ ). The solvent was evaporated and the residue was chromatographed on alumina using ethyl acetate as eluent. The crystalline product (1.0 g) was recrystallized from n-hexane to give 0.59 g, mp 73-76.5 ° C.

Example VIII. N-Ethyl-1-hexyl-4-phenyl-4-piperidinecarboxamide (compound of formula 2).

This compound was prepared as described above from ethyl 1-hexyl-4-phenyl-4-piperidinecarboxylate hydrochloride (3.54 g, 10 mmol) and ethylamine 2.25 g, 50 mmol). Response time 2 days. The crude product (1.0 g) was recrystallized from diisopropyl ether to give 0.81 g, m.p. 92-94 ° C. M.p. hydrochloride 211 - 223 ° C (from 2% aqueous acetone).

Example IX. General method for preparing compounds of formula 4.

Oxalyl chloride (4 ml) was added dropwise with stirring to a solution of piperidinecarboxylic acid (compounds of formula 3) (5-6 mmol) in CH 2 Cl 2 (20 ml). The reaction mixture was stirred at 50 ° C for 2 hours. The solvent was evaporated, a few ml of toluene was added and the solvent was evaporated again. The residue was dissolved in CH 2 O 2 (10 ml) and the stirred solution was added dropwise to a solution of the appropriate amine (35-42 mmol) in CH 2 O 2 (20 ml), cooled with ice water. The reaction mixture was then stirred for several hours at room temperature. The mixture was then shaken with 1N NaOH (20 ml) and once with water, dried (K 2 CO 3) and the solvent was evaporated.

In a few cases, the crude base was further purified, for example by chromatography, prior to conversion to the hydrochloride salt.

Some of the new compounds are shown in Table 1.

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Table 1 Compound of formula 4

Relationship R1 R2 R3 TT ° C 1 CH3 H. C4H _e 73 - 76.5 2 C6H13 H. CH3 252 - 254 3 C6H13 H. C2H5 221-223 4 C6H13 H. CH / CH 3/2 145 - 148 5 C6H13 CH3 CH 3 155.5 - 158.5 6 C6H13 CH3 C2H _S 137- 141 7 C6H13 C2H3 C2H5 151 - 154 8 C6H13 / CH2 / 5 217-219 9 C2H5O / CH2 / 4 CH3 CH3 125 - 128 10 C 2 H 5O / CH 2/4 CH3 C2H5 11-117 11 C2H3O / CH2 / 4 / CH2 / 5 130- 132 12 C 2H 5O CH 2 -CH 2 C 2H 5 C2H5 142- 144 13 C 3 H 7 O / CH 2/2 C2H5 C2H5 14 C4H9O / CH2 / 2 C 2H 5 C2H5

Example X. Pharmaceutical preparations.

To prepare a pharmaceutical formulation, the new compound is dissolved in an injectable liquid diluent. The preparations used are aqueous solutions containing 2.5 to 40.0 mg / ml of active compound, calculated as the hydrochloride.

Example XI. Biological research.

Spinal anesthesia.

The efficacy of the compounds according to the invention in spinal anesthesia was tested in mice. There were six animals in each group. The reference compounds used were pethidine, the starting compound for Compounds No. 2 (-8), namely ethyl-1-hexyl-4-phenyl-apiperidinecarboxylate hydrochloride (Example 1) and 9 (and 10) namely ethyl hydrochloride 1 (Example 2), known from the cited above J. Med. Chem. The results are summarized in Table 2 4-piperidinecarboxylate below.

Table 2

Mean duration (min) of motor anesthesia and full analgesia (tail pulling) in mice after subarachnoid injection of 5 µl of test solution

The periods were counted from the moment of injection

Compound No. in Table 1 or the Example Concentration % Motor anesthesia Duration Tail pull min 1 2 3 4 3 1 10 15 4 14 35 5 14 twenty 6 twenty 40 7 27 50 8 19 40 9 3 10 10 6 10 11 6 10 12 3 10 AND 15 40 II 5 25 3 2 22 thirty

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1 2 3 4 4 24 thirty 5 21 25 6 36 55 7 48 85 8 ' 49 > 120 9 6 10 10 7 10 11 12 35 12 6 10 II 10 15 Pethidine 4 15 1 4 17 twenty Pethidine 10 25

1) The animals were irritated, squeaking.

As can be seen from Table 2, the new compounds have a better local anesthetic effect than the known analgesic drug pethidine. Since a local anesthetic effect is combined with a good analgesic effect, the new compounds are more useful than pethidine. They can also replace painkiller / anesthetic combinations with good results.

The best way to use the invention currently known is the use of compounds 6 or 7.

Scheme

Publishing Department of the UP RP. Circulation of 90 copies. Price: PLN 10,000

Claims (4)

Patent claims 1. A method for the preparation of new 4-phenylo-4-piperidinecarboxamide derivatives of the general formula 4, in which R 1 is an alkyl group of 2 - 6 carbon atoms or an alkoxyalkyl group of the formula R 4O (CH 2) m-, in which R 4 is a group an alkyl group of 1-4 carbon atoms and m is equal to 2,3 or 4, R2 and R3 are independently of each other an alkyl group of up to 6 carbon atoms, or R2 and R3 together form a chain of formula (CH2) m wherein n is 4.5 or 6, or one of R 2 and R 3 is hydrogen and the other is a straight or branched alkyl group with 16 carbon atoms or pharmacologically acceptable salts thereof, characterized in that a) an ester or a nitrile of formula I in which R1 is as defined above and A is -CN or -CO2C2H5 is hydrolyzed to give the corresponding acid of formula I, wherein R1 is as defined above, which is then reacted with 1) oxalyl chloride and 2) a suitable amine of formula R3 (R2) NH in which R2 and R3 are as defined; or b) a compound of formula 1 in which R1 is as defined above and A is a group -CO2C2H5 is reacted with an amine of formula R2NH2 to give a compound of formula 2 in which R1 and R2 are as defined above, i.e. Formula 4 wherein R2 or R3 is hydrogen. 2. The method according to p. The process of claim 1, wherein the compound of formula I and the amine are used, wherein R1, R2 and R3 are alkyl groups. 3. The method according to p. The process of claim 2, wherein the compound of formula 1 is a hexyl group and an amine in which R2 is a methyl group and R3 is an ethyl group. 4. The method according to p. The process of claim 2, wherein the compound of formula 1 is a hexyl group, and an amine, wherein R2 and R3 are ethyl groups.